A technique of manufacturing a layered block structure id as shown in FIGS. 11 and 13, for example, has been already disclosed (See Japanese Patent Application No. Hei 6-103602). According to this technique, the layered block structure 1d is manufactured by the steps of forming fold lines like the inverted letter V, to which a directional folding property (i.e., an inclination to easily fold a corrugated fiberboard sheet) is imparted so as to allow the corrugated fiberboard sheet to fold in the shape of the inverted letter V (in a convex shape), and fold lines like the letter V, to which a directional folding property is imparted so as to allow the corrugated fiberboard sheet to fold in the shape of the letter V (in a concave shape), the two types of fold lines being parallel to each other in an alternating arrangement on the corrugated fiberboard sheet. The corrugated fiberboard sheet is then folded along the fold lines into a zigzag shape.
In addition, a technique of manufacturing a hollow block structure 1e as shown in FIGS. 14 and 15, for example, is disclosed in Japanese Patent Application No. Hei 7-237405. According to this technique, the hollow block structure 1e is manufactured by the steps of forming a plurality of fold lines like the inverted letter V and a plurality of fold lines like the letter V in parallel to each other in an alternating arrangement on a corrugated fiberboard sheet, and then folding the corrugated fiberboard sheet along the fold lines.
The layered or hollow block structure as described above is used as a frame structure or a cushioning material for packaging, a core material for a heat-insulating panel, a carrier for carrying adsorbents or the like.
In general, a corrugated fiberboard sheet is fabricated into a box by the steps of forming fold lines on the corrugated fiberboard sheet by pressing, and then folding the sheet along the fold lines.
In case of fabricating the corrugated fiberboard sheet into a box, the process of folding the sheet along the fold lines does not require high accuracy, and as a result, it is sufficient to form the folds by means of pressing. However, in the case where a layered or hollow block structure as described above is to be manufactured for the above purposes, there is a demand that such a block structure should be exact in shape and size according to the design. Thus, it is not possible to manufacture a block structure, which is fit for the above purposes, only by forming the fold lines in a manner similar to that in case of fabricating the corrugated fiberboard sheet into a box.
In the case where a layered block is manufactured by folding a corrugated fiberboard sheet in a zigzag shape along fold lines formed in advance on the corrugated fiberboard sheet, or a hollow block is manufactured by folding the corrugated fiberboard sheet, the following designs are generally adopted for fold lines, along which the corrugated fiberboard sheet is capable of being folded more accurately.
As shown in FIG. 8, for instance, in a first design fold lines 1a like the inverted letter V and fold lines 1b like the letter V are formed in parallel to each other, alternating between the two faces of the fiberboard sheet, in a halfway incised state (i.e., with cuts extending halfway through the thickness of the corrugated fiberboard sheet). The fold line cuts 1a, 1b intersect corrugated fiberboard flutes 10 and, subsequently, a directional folding property is given to each of the folds 1a, 1b by an appropriate folding mechanism (not shown).
As the result of giving the directional folding as described above, the fold lines 1a of the corrugated fiberboard sheet 1 shown in FIG. 8 take the shape of the inverted letter V, while the fold lines 1b take the shape of the letter V.
Japanese Utility Model Laid-open No. Sho 49-100981 shows a second design in FIG. 9 wherein halfway-incised fold lines 1a like the inverted letter V and fold lines 1b like the letter V are formed in parallel to each other in an alternate arrangement on a corrugated fiberboard sheet 1 such that the fold lines 1a, 1b intersect flutes. Each fold line 1b like the letter V is composed of a long linear cut 10a penetrating the sheet 1, and hinge portions 10b, 10b formed by compressing (crushing) the corrugated fiberboard sheet 1. A short auxiliary cut portion 10c, which extends perpendicularly to each cut 10a and penetrates the corrugated fiberboard sheet 1, is formed at each end of the cut 10a.
After the fold lines 1a, 1b described above are formed on the corrugated fiberboard sheet 1, a directional folding property is given to the sheet 1 along the fold lines 1a by imparting hinge portions 10b with the shape of the inverted letter V, while a directional folding property is given to the sheet 1 along the fold lines 1b by imparting hinge portions with the shape of the letter V, as shown in FIG. 10, by the use of an appropriate folding mechanism (not shown).
As the result of imparting the directional folding to the sheet 1 as described above, an inclination of the sheet to fold into the shape of the letter V is given to non-cut portions 10b of the fold lines 1b. Thus, when a transverse external force as viewed in FIG. 10 is applied to the sheet 1 so as to act in a direction perpendicular to the fold lines 1a, 1b, the sheet 1 is folded along the fold lines 1a, 1b as shown in FIG. 11, and as a result, the block structure id is manufactured.
The auxiliary cut portions 10c are formed in order to prevent the ends of the cut portions 10a of the sheet 1 from being broken when the directional folding property is given to the sheet 1 along the folds 1b.
A third design has been disclosed in International Laid-open No. W095/31330 and will be described with reference to FIG. 12. Halfway-incised fold lines 1a like the inverted letter V and fold lines 1b like the letter V are formed in parallel to each other in an alternate arrangement on a corrugated fiberboard sheet 1 such that the fold lines 1a, 1b intersect flutes 10. Each fold line 1b like the letter V is composed of linear cut portions 10a penetrating the corrugated fiberboard sheet 1, and hinge portions 10b formed by compressing (crushing) the corrugated fiberboard sheet 1. A short auxiliary cut portion 10d, which intersects each cut portion 10a to make an acute angle with the cut portion 10a and penetrates the corrugated fiberboard sheet 1, is formed at each end of the cut portion 10a.
The layered block structure id as shown in FIG. 13 is manufactured by imparting directional folding properties to the fold lines 1a, 1b, and then folding the corrugated fiberboard sheet 1 along the folds 1a, 1b.
The hollow structures shown in FIG. 14 or 15 are also manufactured by folding the sheet 1 along the fold lines 1a, 1b, and then bonding the portions folded along the fold lines 1a and portions folded along the fold lines 1b respectively together.
According to the first design described above, when the fold lines 1a, 1b are formed in the corrugated fiberboard sheet 1, it is necessary to make a cutting part (not shown) bite into both the surfaces of the sheet 1. However, a die cutter (not shown) ordinarily used for incising a corrugated fiberboard sheet is designed for the cutting part to bite into one surface of the corrugated fiberboard sheet 1 traveling along a line. Thus, when making an attempt to form a large number of fold lines 1a, 1b in the sheet 1 through one process, a specially-designed die cutter is needed, increasing the cost of the processing equipment.
On the other hand, in formation of the folds 1a on the corrugated fiberboard sheet 1 by one pass of the sheet 1 through a die cutter on a line, and subsequent formation of the folds 1b by passing the sheet 1 through the die cutter again after the sheet 1 is turned over, the required process steps are increased in number. In addition, due to the increase of equipment for adjusting the positions of the fold lines 1b, and other associated equipment, the manufacturing cost is increased.
Further, when a large number of fold lines 1a like the inverted letter V and a large number of fold lines 1b like the letter V as shown in FIG. 8 are formed on the corrugated fiberboard sheet 1, and directional folding properties are given to these folds, elasticity is lost in the folded portions to make it hard to fold or bend the corrugated fiberboard sheet in the final process, and it is difficult to fabricate the corrugated fiberboard sheet into a block structure again in case of reusing the corrugated fiberboard sheet.
According to the second design described above, it is possible to overcome the problems with the first design. However, the auxiliary cut portions 10c respectively extend perpendicularly to the cut portion 10a and are formed linearly, and all the non-cut portions 10b forming the hinge portions in the folds 1b are of equal length L within a width w corresponding to the length of each auxiliary cut portion 10c, as shown in FIG. 9. Thus, when directional folding properties are given to the sheet 1 along the folds 1b the hinge portions 10b formed as the non-cut portions are not always folded in alignment with the cut portion 10a with accuracy, and are somewhat offset from the cut portion 10a in some cases. Further, when the corrugated fiberboard sheet 1 is folded or bent after the directional folding properties are given to the sheet along the folds, the hinge portions 10b are bent somewhat away from the cut portion 10a in some cases. Therefore, when the sheet 1 is folded in layers as shown in FIG. 11, the folds 1a, 1b of the sheet 1 are slightly offset from each other as shown by arrows 1c in FIG. 11, and a layered block structure 1d easily gets out of shape. Thus, in some cases, it is not possible to manufacture a block structure 1d of a shape which is within the range of design tolerance.
According to the third design, since the auxiliary cut portion 10d at each end of the cut portion 10a has an angular shape pointed toward an adjacent hinge portion 10b, the pointed end of each auxiliary cut portion 10d serves as a guide in folding, and as a result, it is possible to fold or bend the corrugated fiberboard sheet 1 along the fold lines 1b with accuracy. However, in the case where the cut portions 10a respectively having the auxiliary cut portions 10d as shown in FIG. 12 are formed on the corrugated fiberboard sheet 1, it is necessary to manufacture a die cutting part (not shown) of a planar shape corresponding to the planar shape of each cut portion 10a by means of welding. The problem with manufacture of the die cutting part by means of welding is that the manufacturing cost of the die cutter (not shown) is increased.
Further, when a block structure is manufactured by folding the corrugated fiberboard sheet 1 along the fold lines 1a, 1b as shown in FIG. 13, or by bending the corrugated fiberboard sheet 1 along the fold lines 1a, 1b as shown in FIG. 14 or 15, a linerboard of the corrugated fiberboard sheet 1 protrudes from portions of the auxiliary cut portions 10d in folds formed at the fold lines 1b. The raised linerboard portions are sometimes obstructive to handling or broken when brought by contact with other objects. Sections of the corrugated fiberboard flutes 10 at portions of the cuts 10a are largely exposed, and as a result, the external appearance of the block structure 1d or 1e is damaged in some cases.
It is an object of the present invention to provide a design for fold lines shaped like the letter V, along which a corrugated fiberboard sheet is capable of being folded more accurately in manufacturing a layered block structure or a hollow block structure, in which a plurality of hollow portions are connected together by forming fold lines in the corrugated fiberboard sheet. and then folding or bending the corrugated fiberboard sheet along the fold lines.
Another object of the present invention is to provide a fold line structure for a corrugated fiberboard, in which corrugated fiberboard flutes are not largely exposed at the folds, and less linerboard protrudes from the folds, upon fabricating the corrugated fiberboard sheet into the block structure described above.
A further object of the present invention is to provide a fold line structure for a corrugated fiberboard, in which fold lines like the letter V, show sufficient elasticity for reuse of a corrugated fiberboard sheet.